This invention relates to compounds able to modulate one or more inorganic ion receptor activities.
The references provided herein are not admitted to be prior art to the claimed invention.
Certain cells in the body respond not only to chemical signals, but also to ions such as extracellular calcium ions (Ca2+). Extracellular Ca2+ is under tight homeostatic control and regulates various processes such as blood clotting, nerve and muscle excitability, and proper bone formation.
Calcium receptor proteins enable certain specialized cells to respond to changes in extracellular Ca2+ concentration. For example, extracellular Ca2+ inhibits the secretion of parathyroid hormone (PTH) from parathyroid cells, inhibits bone resorption by osteoclasts, and stimulates secretion of calcitonin from C-cells.
PTH is the principal endocrine factor regulating Ca2+ homeostasis in the blood and extracellular fluids. PTH, by acting on bone and kidney cells, increases the level of Ca2+ in the blood. This increase in extracellular Ca2+ then acts as a negative feedback signal, depressing PTH secretion. The reciprocal relationship between extracellular Ca2+ and PTH secretion forms an important mechanism maintaining bodily Ca2+ homeostasis.
Extracellular Ca2+ acts directly on parathyroid cells to regulate PTH secretion. The existence of a parathyroid cell surface protein which detects changes in extracellular Ca2+ has been confirmed. (Brown et al., Nature 366:574, 1993.) In parathyroid cells, this protein, the calcium receptor, acts as a receptor for extracellular Ca2+, detects changes in the ion concentration of extracellular Ca2+, and initiates a functional cellular response, PTH secretion.
Extracellular Ca2+ can exert effects on different cell functions, reviewed in Nemeth et al., Cell Calcium 11:319, 1990. The role of extracellular Ca2+ in parafollicular (C-cells) and parathyroid cells is discussed in Nemeth, Cell Calcium 11:323, 1990. These cells were shown to express similar calcium receptors. (See Brown et al., Nature 366:574, 1993; Mithal et al., J. Bone Miner. Res. 9, Suppl. 1, s282, 1994; Rogers et al., J. Bone Miner. Res. 9, Suppl, 1, s409, 1994; Garrett et al., Endocrinology 136:5202-5211, 1995.)
The ability of various molecules to mimic extracellular Ca2+ in vitro is discussed in references such as Nemeth et al., in xe2x80x9cCalcium-Binding Proteins in Health and Disease,xe2x80x9d 1987, Academic Press, Inc., pp. 33-35; Brown et al., Endocrinology 128:3047, 1991; Chen et al., J. Bone Miner. Res. 5:581, 1990; and Zaidi et al., Biochem. Biophys. Res. Commun. 167:807, 1990.
Nemeth et al., PCT/US92/07175, International Publication Number WO 93/04373, Nemeth et al., PCT/US93/01642, International Publication Number WO 94/18959, and Nemeth et al., PCT/US94/12117, International Publication Number WO 95/11211, describe various compounds which can modulate the effect of an inorganic ion receptor.
The present invention features compounds able to modulate one or more activities of an inorganic ion receptor and methods for treating diseases or disorders using such compounds. Preferred compounds can mimic or block the effect of extracellular calcium on a cell surface calcium receptor.
Inorganic ion receptor activities are those processes brought about as a result of inorganic ion receptor activation. Such processes include the production of molecules which can act as intracellular or extracellular messengers.
Inorganic ion receptor-modulating compounds include ionomimetics, ionolytics, calcimimetics, and calcilytics. Ionomimetics are compounds which mimic (i.e., evoke or potentiate) the effects of an inorganic ion at an inorganic ion receptor. Preferably, the compound affects one or more calcium receptor activities. Calcimimetics are ionomimetics which affect one or more calcium receptor activities.
Ionolytics are compounds which block (i.e., inhibit or diminish) one or more activities caused by an inorganic ion at an inorganic ion receptor. Preferably, the compound affects one or more calcium receptor activities. Calcilytics are ionolytics which block one or more calcium receptor activities evoked by extracellular calcium.
Ionomimetics and ionolytics may bind at the same receptor site as the native inorganic ion ligand binds or can bind at a different site (e.g., an allosteric site). For example, NPS R-467 binding to a calcium receptor results in calcium receptor activity and, thus, NPS R-467 is classified as a calcimimetic. However, NPS R-467 binds to the calcium receptor at a different site (i.e., an allosteric site) than extracellular calcium.
A measure of the effectiveness of a compound to modulate receptor activity can be determined by calculating the EC50 or IC50 for that compound. The EC50 is the concentration of a compound which causes a half-maximal mimicking effect. The IC50 is the concentration of a compound which causes a half-maximal blocking effect. EC50 and IC50 values for compounds at a calcium receptor can be determined by assaying one or more of the activities of extracellular calcium at a calcium receptor. Examples of assays for measuring EC50 and IC50 values are described Nemeth et al., PCT/US93/01642, International Publication Number WO 94/18959, and Nemeth et al., PCT/US92/07175, International Publication Number WO 93/04373, (both of these publications are hereby incorporated by reference here) and below. Such assays include oocyte expression assays and measuring increases in intracellular calcium ion concentration ([Ca2+]i) due to calcium receptor activity. Preferably, such assays measure the release or inhibition of a particular hormone associated with activity of a calcium receptor.
An inorganic ion receptor-modulating compound preferably selectively targets inorganic ion receptor activity in a particular cell. For example, selective targeting of a calcium receptor activity is achieved by a compound exerting a greater effect on a calcium receptor activity in one cell type than at another cell type for a given concentration of compound. Preferably, the differential effect is 10-fold or greater as measured in vivo or in vitro. More preferably, the differential effect is measured in vivo and the compound concentration is measured as the plasma concentration or extracellular fluid concentration and the measured effect is the production of extracellular messengers such as plasma calcitonin, parathyroid hormone, or plasma calcium. For example, in a preferred embodiment, the compound selectively targets PTH secretion over calcitonin secretion.
Preferably, the compound is either a calcimimetic or calcilytic having an EC50 or an IC50 at a calcium receptor of less than or equal to 5 xcexcM, and even more preferably less than or equal to 1 xcexcM, 100 nmolar, 10 nmolar, or 1 nmolar using one of the assays described below. More preferably, the assay measures intracellular Ca2+ in HEK 293 cells transformed with nucleic acid expressing the human parathyroid calcium receptor and loaded with fura-2. Lower EC50 or IC50 values are advantageous since they allow lower concentrations of compounds to be used in vivo or in vitro. The discovery of compounds with low EC50 and IC50 values enables the design and synthesis of additional compounds having similar or improved potency, effectiveness, and/or selectivity.
Thus, a first aspect the invention features an inorganic ion receptor-modulating compound having the formula: 
wherein Ar1 is either optionally substituted naphthyl, optionally substituted phenyl, or an optionally substituted heterocyclic aryl, where up to 5 substituents may be present and each substituent is independently selected from the group consisting of: alkyl, alkenyl, halogen, alkoxy, thioalkyl, methylene dioxy, haloalkyl, haloalkoxy, OH, CH2OH, CONH2, CN, acetoxy, N(alkyl)2, phenyl, phenoxy, benzyl, benzyloxy, xcex1,xcex1-dimethylbenzyl, NO2, CHO, CH3CH(OH), acetyl, OCH2COOH, and ethylene dioxy;
Ar2 is either optionally substituted naphthyl, optionally substituted phenyl, or an optionally substituted heterocyclic aryl, where up to 5 substituents may be present and each substituent is independently selected from the group consisting of: alkyl, alkenyl, halogen, alkoxy, thioalkyl, methylene dioxy, haloalkyl, haloalkoxy, OH, CH2OH, CONH2, CN, OCH2COOH, ethylene dioxy, and acetoxy;
q is 0, 1, 2, or 3;
R1 is either H or alkyl; and
R2 and R3 are each independently either hydrogen, alkyl, or together cycloalkyl or cycloalkenyl;
and pharmaceutically acceptable salts and complexes thereof.
Preferably, the compound is an ionomimetic which modulates one or more inorganic ion receptor activities, more preferably the compound is a calcimimetic.
xe2x80x9cAlkenylxe2x80x9d refers to a hydrocarbon chain having 2-6 carbons and at least one double-bond which may be a straight chain, branched, or non-aromatic cyclic. Preferably, the alkenyl has 2-4 carbon atoms.
xe2x80x9cAlkylxe2x80x9d refers to a saturated hydrocarbon having 1-6 carbons which may be a straight chain, branched, or cyclic. Preferably, the alkyl has 1-4 carbon atoms.
xe2x80x9cAlkoxyxe2x80x9d refers to xe2x80x9cO-alkyl,xe2x80x9d where xe2x80x9cOxe2x80x9d is an oxygen joined to an alkyl.
xe2x80x9cCycloalkenylxe2x80x9d refers to a non-aromatic cyclic hydrocarbon chain having 3-12 carbons and at least one double-bond, and includes multiple ring structures. Preferably, the cycloalkenyl has 3 to 6 carbon atoms.
xe2x80x9cCycloalkylxe2x80x9d refers to a saturated cyclic hydrocarbon chain having 3-12 carbons, and includes multiple ring structures. Preferably, the cycloalkyl has 3 to 6 carbon atoms.
xe2x80x9cThioalkylxe2x80x9d refers to xe2x80x9cS-alkyl,xe2x80x9d where xe2x80x9cSxe2x80x9d is a sulfur joined to an alkyl.
xe2x80x9cHaloalkylxe2x80x9d refers to an alkyl substituted with at least one halogen. Preferably, only the terminal carbon of the haloalkyl is substituted with a halogen and 1 to 3 halogens are present. More preferably, the haloalkyl contains 1 carbon. Preferably, the halogen substitutions are either Cl or F.
xe2x80x9cHaloalkoxyxe2x80x9d refers to xe2x80x9cO-haloalkyl,xe2x80x9d where xe2x80x9cOxe2x80x9d is an oxygen joined to a haloalkyl.
xe2x80x9cHeterocyclic arylxe2x80x9d refers to an aryl ring system having 1 to 3 heteroatoms as ring atoms in a heteroaromatic ring system and the remainder of the ring atoms are carbon atoms. Suitable heteroatoms include oxygen, sulfur, and nitrogen. Preferably, the heterocyclic aryl ring system is mono- or bicyclic. More preferably, the heterocyclic aryl is either furanyl, thiofuranyl (also known as xe2x80x9cthienylxe2x80x9d), benzofuranyl or benzothiofuranyl (also known as xe2x80x9cbenzothienylxe2x80x9d).
Another aspect of the present invention features an inorganic ion receptor-modulating compound having the formula: 
Where Ar1, Ar2, R2 and R3 are as described for Structure I compounds;
R7 is either hydrogen, alkyl or phenyl;
R8 is either hydrogen, or alkyl;
R9 is either hydrogen, alkyl or phenyl; and pharmaceutically acceptable salts and complexes thereof.
Preferably, the compound is an ionomimetic modulating one or more inorganic ion receptor activities, more preferably the compound is a calcimimetic.
Another aspect of the present invention features a pharmaceutical composition made up of an inorganic ion receptor-modulating compound described herein and a physiologically acceptable carrier. A xe2x80x9cpharmacological compositionxe2x80x9d refers to a composition in a form suitable for administration into a mammal, preferably a human. Preferably, the pharmaceutical composition contains a sufficient amount of a calcium receptor-modulating compound in a proper pharmaceutical form to exert a therapeutic effect on a human.
Considerations concerning forms suitable for administration are known in the art and include toxic effects, solubility, route of administration, and maintaining activity. For example, pharmacological compositions injected into the blood stream should be soluble.
Pharmaceutical compositions can also be formulated as pharmaceutically acceptable salts (e.g., acid addition salts) and complexes thereof. The preparation of such salts can facilitate the pharmacological use of a compound by altering its physical characteristics without preventing it from exerting a physiological effect.
Another aspect the present invention features a method for treating a patient by using inorganic ion receptor-modulating compounds described herein. The method involves administering to the patient a pharmaceutical composition containing a therapeutically effective amount of an inorganic ion receptor-modulating compound. In a preferred embodiment, the disease or disorder is treated by administering to the patient a therapeutically effective amount of a calcium receptor-modulating compound.
Inorganic ion receptor-modulating compounds, and compositions containing such compounds, can be used to treat different types of patients. A xe2x80x9cpatientxe2x80x9d refers to a mammal in which compounds able to modulate inorganic ion receptor activity will have a beneficial effect including a beneficial prophylactic effect. Suitable patients can be diagnosed using standard techniques known to those in the medical profession.
Preferably, a patient is a human having a disease or disorder characterized by one more of the following: (1) abnormal inorganic ion homeostasis, more preferably abnormal calcium homeostasis; (2) an abnormal level of a messenger whose production or secretion is affected by inorganic ion receptor activity, more preferably affected by calcium receptor activity; and (3) an abnormal level or activity of a messenger whose function is affected by inorganic ion receptor activity, more preferably affected by calcium receptor activity.
Diseases characterized by abnormal calcium homeostasis include hyperparathyroidism, osteoporosis and other bone and mineral-related disorders, and the like (as described, e.g., in standard medical text books, such as xe2x80x9cHarrison""s Principles of Internal Medicinexe2x80x9d). Such diseases are treated using calcium receptor-modulating compounds which mimic or block one or more of the effects of extracellular Ca2+ on a calcium receptor.
By xe2x80x9ctherapeutically effective amountxe2x80x9d is meant an amount of a compound which relieves to some extent one or more symptoms of a disease or disorder in the patient; or returns to normal either partially or completely one or more physiological or biochemical parameters associated with or causative of the disease or disorder. Thus, a therapeutically effective amount can be an amount effective to prophylactically decrease the likelihood of the onset of a disease or disorder.
In a preferred embodiment, the patient has a disease or disorder characterized by an abnormal level of one or more calcium receptor-regulated components and the compound is active on a calcium receptor of a cell selected from the group consisting of: parathyroid cell, bone osteoclast, juxtaglomerular kidney cell, proximal tubule kidney cell, distal tubule kidney cell, central nervous system cell, peripheral nervous system cell, cell of the thick ascending limb of Henle""s loop and/or collecting duct, keratinocyte in the epidermis, parafollicular cell in the thyroid (C-cell), intestinal cell, platelet, vascular smooth muscle cell, cardiac atrial cell, gastrin-secreting cell, glucagon-secreting cell, kidney mesangial cell, mammary cell, beta cell, fat/adipose cell, immune cell, GI tract cell, skin cell, adrenal cell, pituitary cell, hypothalamic cell, and cell of the subfornical organ.
More preferably, the cells are chosen from the group consisting of: parathyroid cell, central nervous system cell, peripheral nervous system cell, cell of the thick ascending limb of Henle""s loop and/or collecting duct in the kidney, parafollicular cell in the thyroid (C-cell), intestinal cell, GI tract cell, pituitary cell, hypothalamic cell, and cell of the subfornical organ.
In a preferred embodiment, the compound reduces the level of parathyroid hormone in the serum of the patient. More preferably, the level is reduced to a degree sufficient to cause a decrease in plasma Ca2+. Most preferably, the parathyroid hormone level is reduced to that present in a normal individual.
Patients in need of treatment using the compounds described by the present invention can be diagnosed by standard medical techniques, such as blood or urine analysis. Examples of such medical techniques include detecting a deficiency of protein whose production or secretion is affected by changes in inorganic ion concentrations, and by detecting abnormal levels of inorganic ions or hormones which effect inorganic ion homeostasis.
Various examples are used throughout the application. These examples are not intended in any way to limit the claimed invention.
Other features and advantages of the invention will be apparent from the following figures, detailed description of the invention, examples, and the claims.